Device for collecting solar energy by means of a concentrator of the nonimaging type

ABSTRACT

The present invention concerns a device for collecting solar energy by means of a concentrator of the nonimaging type and a receiver for the transfer of energy by heat exchange with a fluid which operates, independently, a thermodynamic cycle for the exploitation of energy, said concentrator comprising an inlet area, an underlying outlet area and an inner space between said inlet area and said outlet area; said receiver being positioned under said concentrator and said inner space of the concentrator and said receiver being connected by said outlet area, characterized in that said inner space of the concentrator and said receiver are in fluid communication through said outlet area, a plurality of solid particles are present inside said receiver, and said device for collecting solar energy comprises means apt to take a part of said solid particles from said receiver and to put them from below inside said inner space of said concentrator, said solid particles subsequently returning, by gravity, into said receiver, passing through said outlet area.

The present invention concerns a device for collecting solar energy bymeans of a concentrator of the nonimaging type.

The invention is referred to the field of devices for collecting solarenergy of the nonimaging type (NIO), such as CPC (Coumpond ParabolicConcentrator), and in particular to a new way of operating and using thesame.

It is known that the solar radiation reaching the surface of the Earthhas mean values of thermal flux around 1 kWh/m²: such a value is too lowand economically non convenient to be exploited in pants of productionof electric energy.

As a consequence, starting from the need to concentrate high densityfluxes over small surfaces, developed the first studies on theconcentration optical systems and, in particular, those dedicated tononimaging optics (NIO). In fact, such concentration devices have theadvantage of optimizing the transmission of energy from a source to areceiver, instead of forming the typical image of the optic systems (IO)and with no relevance in the field of energy transfer.

The CPC (Compound Parabolic Concentrator), evolution of the coneconcentrator, belongs to the class of nonimaging concentrators: reachingconcentration values very closet o those of the ideal concentrator, andis able to concentrate and transfer towards its outlet section almostthe entire energy of the beams of rays tapping on the opening, with anangle that is lower or the same of the acceptance angle θ for which theconcentrator was designed.

The receiver, device designed to absorb the sun radiation, isrepresented generally as a separate unit and, in its various forms andembodiments, if positioned at the level of the ground, is generallycovered exactly by a nonimaging concentrator (very frequently a CPC)having the task of increasing the density of concentration. The receiverdoes not have any interaction with the concentration system, withoutmodifying, in any way, its operation.

WO2014/038553 discloses a device for collecting solar energy by means ofa concentrator of the nonimaging type, wherein inside the receiver isoriginated a fluidized bed of solid particles. Solid particles areheated by means of exposure to concentrated sun radiation andsubsequently withdrawn and sent to a heat exchanger. The fluidizationgas is withdrawn separately from the solid particles and sent to a heatexchanger for pre-heating of the same gas fed to the fluidized bed.

In actual situations, nonimaging systems behave differently with respectto the ideal situation. In fact, according to experimental tests, a partof rays with an incidence angle that is very close to the acceptanceangle 8 have an inverse behavior compared to that expected and generatetransmission curves with inflection points more or less accentuated.

Moreover, all the beams of rays with angle higher than the acceptanceangle θ are rejected and pass through the inlet section abandoning theCPC.

The conveying of the solar rays in the NIO optics within the limits ofthe acceptance angle results in the need for extremely expensivepointing systems of sun radiation, with a consequent increase in costsof the system.

There is therefore the need to improve the behavior of NIO systems withrespect to the transmission of sun radiation on to the receiver, whenthe beams of rays arrive with an angle higher or close to the acceptanceangle.

In this context it is included the solution according to the presentinvention, which aims to provide a new method and system to optimizeenergy harvesting in a NIO system.

These and other results are obtained according to the present inventionby proposing to enter inside the volume delimited by the NIO system,such as a CPC, in the opposite direction to that of concentration, afair number of solid particles, so that the latter can intercept andabsorb up to thermodynamic equilibrium and during the multiple andrandom locations occupied in the fall or ascent phase, the sun radiationthat enters the CPC.

A purpose of the present invention is therefore to provide a device forcollecting solar energy by means of a concentrator of the nonimaging(NIO) type suitably coupled with a receiver, which allows to overcomethe limitations of NIO systems according to the prior art and to obtainthe previously described technical results.

A further aim of the invention is that said device for collecting solarenergy by means of a concentrator of the nonimaging type can be madewith low costs, with regard to both the production costs and themanagement costs.

Another object of the invention is to propose a device for collectingsolar energy by means of a concentrator of the nonimaging type that issimple, safe and reliable.

It is therefore a specific object of the present invention a device forcollecting solar energy by means of a concentrator of the nonimagingtype and a receiver for the transfer of energy by heat exchange with afluid which operates, independently, a thermodynamic cycle for theexploitation of energy, said concentrator comprising an inlet area, anunderlying outlet area and an inner space between said inlet area andsaid outlet area; said receiver being positioned under said concentratorand said inner space of the concentrator and said receiver beingconnected by said outlet area, wherein said inner space of theconcentrator and said receiver are in fluid communication through saidoutlet area, a plurality of solid particles are present inside saidreceiver, and said device for collecting solar energy comprises meansapt to take a part of said solid particles from said receiver and to putthem from below inside said inner space of said concentrator, said solidparticles subsequently returning, by gravity, into said receiver,passing through said outlet area.

In particular, according to the invention, said means apt to take saidsolid particles from said receiver and to put them from below insidesaid inner space of said concentrator comprise an input device.

Preferably, according to the invention, said means apt to take saidsolid particles from said receiver and to put them from below insidesaid inner space of said concentrator are made of streams of gases,vapours, or by a combination of the same, apt to raise said solidparticles up to a height comprised between said inlet area and saidoutlet area of the concentrator.

More preferably, according to the invention, said receiver and saidmeans apt to take said solid particles from said receiver and to putthem from below inside said inner space of said concentrator are made ofa spouted bed.

In particular, according to the present invention, said concentrator isa CPC concentrator (Compound Parabolic Concentrator).

Finally, always according to the invention, said solid particles aremade of a material with high solar absorption and low emissivity, suchas metal-type oxides and, preferably, chromite ((Mg,Fe)(Cr,Al)₂O₄).

It is evident the effectiveness of the device of the present invention,which allows to intercept and absorb, by means of the solid particlesplaced inside the volume delimited by the nonimaging system, the sunradiation which enters in the same. By modifying the amount, the heightand the frequency of the jet of particles, it is possible to do so thatthe particles can reach the receiver progressively increasing theirtemperature, up to a level such as to make efficient the heat exchangewith another fluid which operates, independently, a thermodynamic cyclefor the exploitation of energy.

Since, statically, the particles can be in some positions occupied bybeams of rays that, after a series of internal reflections in thenonimaging system, would be thrown to the outside, it is clear that thenew device is able to modify the energy performance of a traditional CPCconcentrator or, more generally, of any nonimaging concentrator.

The present invention will be now described, for illustrative but notlimitative purposes, according to its preferred embodiment, withparticular reference to the figures of the accompanying drawings, inwhich:

FIG. 1 shows a sectional view of a CPC concentrator according to theprior art, and

FIG. 2 shows a sectional view of a device for collecting solar energy bymeans of a concentrator of the nonimaging type according to the presentinvention, applied to a CPC concentrator.

Making preliminarily reference to FIG. 1, in a solar concentrationsystem CPC, indicated as a whole by the reference number 12, with aninlet area 1, an outlet area 2 and an acceptance angle θ, sun raysentering the inlet section with an angle lower than θ, such as forexample the ray indicated by the reference number 5, reach the outletsection 2 and the receiver 3; on the contrary, the ray 4, which presentsan angle of inlet greater than that of acceptance, after a number ofreflections on the walls of the concentrator 12, is rejected and willnever reach the outlet section 2 and, consequently, the receiver 3.

In FIG. 2, a device for collecting solar energy by means of aconcentrator of the nonimaging type according to the present invention,applied to the CPC concentrator 12 already shown with reference to FIG.1, without prejudice to the geometry of the CPC 12 and of the receiver3, provides for an input devices 6 that randomly introduce within theCPC 12 some solid particles 11 taken from the inside of the receiver 3.

Solid particles 11 taken from the inside of the receiver 3 andintroduced within the CPC 12 therefore occupy part of the empty spacedelimited by the CPC 12. For example, the solid particle 8, launchedfrom the input device 6, following the trajectory 7, intercepts the ray4, with inlet angle higher than the acceptance angle, absorbing all orpart of the thermal energy and transporting it, falling back, towardsthe receiver 3. If it had not been intercepted by the solid particle 8,this energy would have been lost, as already explained with reference toFIG. 1, disclosing the operation of the CPCs according to the prior art.

In the same way, also the solid particle 10, launched from the inputdevice 6, following the trajectory 9, intercepts the ray 5, with inletangle lower than the acceptance angle, absorbing all or part of itsthermal energy and transporting it, falling back, towards the receiver3, but in a way completely different from what would happen in a CPCaccording to the prior art.

Other rays, with inlet angle lower than that of acceptance, reach thereceiver 3 and give thermal energy to the solid particles that arelocated inside this receiver. Inside the receiver 3, to optimize theheat exchange, the solid particles may advantageously be kept in motion,for example by generation of a fluidized bed.

It appears evident that, in a device for collecting solar energy bymeans of a concentrator of the nonimaging type according to the presentinvention, the operation of a CPC concentrator 12 is deeply changed bythe presence of the solid particles and that, as a consequence, it ispossible a great improvement of the system performance, since suchparticles make it possible to absorb part of the energy that, in a CPCconcentrator according to the prior art, would be surely lost.

It is also clear that the solid particles, during their ascent anddescent trajectory within the CPC 12, meet a large number of rays andthat the particles themselves, interacting between them, can change thetrajectory imposed on them by the input device 6. Accordingly, the inputdevice 6 is preferably selected from those capable of ensuring a moreuniform possible movement of the particles 11 taken from the receiver 3.

Solid particles 11, according to the invention, will be preferably madeof material with high solar absorption and low emissivity, but anywaythey will be chosen according to the actual operating conditions of thesystem as requested by the receiver 3 for energy recovery.

The input of the particles may be carried out in different ways. Apreferred embodiment provides for the use of a “spouted bed” that,itself acting as receiver, allows to use the “fountain of particles”that is created on top as a true ejector.

However, are also possible mechanical, fluidodynamic or combined systemsdesigned so that the particles do not exit from the top of the CPC 12 orfrom another nonimaging system and occupy, as far as possible, all theavailable volume.

The input process can be continuous or discontinuous and thereforeprogrammed to operate with a certain frequency.

By means of the device for collecting solar energy by means of aconcentrator of the nonimaging type according to the present inventionit is then created a multifocus system, able of differently the thermalenergy transmitted and focused by a traditional NIO system or, inparticular, by a CPC.

In conclusion, the invention can be summarized as a nonimaging systemthe internal volume of which is partially occupied by a series of solidparticles, introduced from the outlet section of the NIO system, able toabsorb the sun radiation entering the NIO system, independently from theacceptance angle.

The present invention has been described for illustrative but notlimitative purposes, according to its preferred embodiments, but it isto be understood that variations and/or modifications may be made bythose skilled in the art without departing from the relative scope ofprotection, as defined by the enclosed claims.

1. Device for collecting solar energy by means of a concentrator of thenonimaging type and a receiver for the transfer of energy by heatexchange with a fluid which operates, independently, a thermodynamiccycle for the exploitation of energy, said concentrator comprising aninlet area, an underlying outlet area and an inner space between saidinlet area and said outlet area; said receiver being positioned undersaid concentrator and said inner space of the concentrator and saidreceiver being connected by said outlet area, wherein said inner spaceof the concentrator and said receiver are in fluid communication throughsaid outlet area, a plurality of solid particles are present inside saidreceiver, and said device for collecting solar energy comprises meansapt to take a part of said solid particles from said receiver and to putthem from below inside said inner space of said concentrator, said solidparticles subsequently returning, by gravity, into said receiver,passing through said outlet area.
 2. Device for collecting solar energyaccording to claim 1, wherein said means apt to take said solidparticles from said receiver and to put them from below inside saidinner space of said concentrator comprise an input device.
 3. Device forcollecting solar energy according to claim 1, wherein said means apt totake said solid particles from said receiver and to put them from belowinside said inner space of said concentrator are made of streams ofgases, vapours, or by a combination of the same, apt to raise said solidparticles up to a height comprised between said inlet area and saidoutlet area of the concentrator.
 4. Device for collecting solar energyaccording to claim 2, wherein said receiver and said means apt to takesaid solid particles from said receiver and put them inside said innerspace of said concentrator are made of a spouted bed.
 5. Device forcollecting solar energy according to claim 1, wherein said concentratoris a CPC concentrator (Compound Parabolic Concentrator).
 6. Device forcollecting solar energy according to claim 1, wherein said solidparticles are made of a material with high solar absorption and lowemissivity.
 7. Device for collecting solar energy according to claim 1,wherein said solid particles are made of oxides of the metallic type. 8.Device for collecting solar energy according to claim 7, wherein saidsolid particles are made of chromite ((Mg,Fe)(Cr,Al)₂O₄).